7,214 research outputs found
Mobility of Dislocations in Aluminum
The velocities of individual dislocations of edge and mixed types in pure aluminum single crystals were determined as a function of appliedâresolved shear stress and temperature. The dislocation velocities were determined from measurements of the displacements of individual dislocations produced by stress pulses of known duration. The BergâBarrett xâray technique was employed to observe the dislocations, and stress pulses of 15 to 108 ÎŒsec duration were applied by propagating torsional waves along the axes of [111]âoriented cylindrical crystals. Resolved shear stresses up to 16Ă10^6 dynesâcm^2 were applied at temperatures ranging from â150° to +70°C, and dislocation velocities were found to vary from 10 to 2800 cmâsec over these ranges of stress and temperature. The experimental conditions were such that the dislocation velocities were not significantly influenced by impurities, dislocation curvature, dislocationâdislocation interactions, or longârange internal stress fields in the crystals. The velocity of dislocations is found to be linearly proportional to the appliedâresolved shear stress, and to decrease with increasing temperature. Qualitative comparison of these results with existing theories leads to the conclusion that the mobility of individual dislocations in pure aluminum is governed by dislocationâphonon interactions. The phononâviscosity theory of dislocation mobility can be brought into agreement with the experimental results by reasonable choices of the values of certain constants appearing in the theory
The design and implementation of the Technical Facilities Controller (TFC) for the Goldstone deep space communications complex
The Technical Facilities Controller is a microprocessor-based energy management system that is to be implemented in the Deep Space Network facilities. This system is used in conjunction with facilities equipment at each of the complexes in the operation and maintenance of air-conditioning equipment, power generation equipment, power distribution equipment, and other primary facilities equipment. The implementation of the Technical Facilities Controller was completed at the Goldstone Deep Space Communications Complex and is now operational. The installation completed at the Goldstone Complex is described and the utilization of the Technical Facilities Controller is evaluated. The findings will be used in the decision to implement a similar system at the overseas complexes at Canberra, Australia, and Madrid, Spain
Engineering vibrationally-assisted energy transfer in a trapped-ion quantum simulator
Many important chemical and biochemical processes in the condensed phase are
notoriously difficult to simulate numerically. Often this difficulty arises
from the complexity of simulating dynamics resulting from coupling to
structured, mesoscopic baths, for which no separation of time scales exists and
statistical treatments fail. A prime example of such a process is vibrationally
assisted charge or energy transfer. A quantum simulator, capable of
implementing a realistic model of the system of interest, could provide insight
into these processes in regimes where numerical treatments fail. We take a
first step towards modeling such transfer processes using an ion trap quantum
simulator. By implementing a minimal model, we observe vibrationally assisted
energy transport between the electronic states of a donor and an acceptor ion
augmented by coupling the donor ion to its vibration. We tune our simulator
into several parameter regimes and, in particular, investigate the transfer
dynamics in the nonperturbative regime often found in biochemical situations
Benchmarking high fidelity single-shot readout of semiconductor qubits
Determination of qubit initialisation and measurement fidelity is important
for the overall performance of a quantum computer. However, the method by which
it is calculated in semiconductor qubits varies between experiments. In this
paper we present a full theoretical analysis of electronic single-shot readout
and describe critical parameters to achieve high fidelity readout. In
particular, we derive a model for energy selective state readout based on a
charge detector response and examine how to optimise the fidelity by choosing
correct experimental parameters. Although we focus on single electron spin
readout, the theory presented can be applied to other electronic readout
techniques in semiconductors that use a reservoir.Comment: 19 pages, 8 figure
Patient-specific CFD models for intraventricular flow analysis from 3D ultrasound imaging : comparison of three clinical cases
Background: As the intracardiac flow field is affected by changes in shape and motility of the heart, intraventricular flow features can provide diagnostic indications. Ventricular flow patterns differ depending on the cardiac condition and the exploration of different clinical cases can provide insights into how flow fields alter in different pathologies. Methods: In this study, we applied a patient-specific computational fluid dynamics model of the left ventricle and mitral valve, with prescribed moving boundaries based on transesophageal ultrasound images for three cardiac pathologies, to verify the abnormal flow patterns in impaired hearts. One case (P1) had normal ejection fraction but low stroke volume and cardiac output, P2 showed low stroke volume and reduced ejection fraction, P3 had a dilated ventricle and reduced ejection fraction. Results: The shape of the ventricle and mitral valve, together with the pathology influence the flow field in the left ventricle, leading to distinct flow features. Of particular interest is the pattern of the vortex formation and evolution, influenced by the valvular orifice and the ventricular shape. The base-to-apex pressure difference of maximum 2 mmHg is consistent with reported data. Conclusion: We used a CFD model with prescribed boundary motion to describe the intraventricular flow field in three patients with impaired diastolic function. The calculated intraventricular flow dynamics are consistent with the diagnostic patient records and highlight the differences between the different cases. The integration of clinical images and computational techniques, therefore, allows for a deeper investigation intraventricular hemodynamics in patho-physiology. (C) 2016 Elsevier Ltd. All rights reserved
Angiotensin II-Induced Hypertension in Apolipoprotein E-Deficient Rats
Abdominal aortic aneurysms (AAAs) are characterized by a weakened vessel wall and a diameter 50% greater than normal. AAA are usually asymptomatic until they are near rupturing, which can be fatal if not treated immediately. Apolipoprotein E-deficient (ApoE) mice are commonly used as a model to study aneurysm growth. Our lab has created a similar model using rats, which are more similar to humans. This study focuses on the analysis of blood pressures collected from ApoE rats for comparison with a known mouse model. Five ApoE rats (1 female, 4 males) received subcutaneous implants of osmotic mini pumps that released a continuous flow of angiotensin II (AngII) at 200 ng/kg/min. AngII is a protein known to increase blood pressure by acting on the renin-angiotensin system. Systolic, diastolic, and mean arterial pressures were measured using a non-invasive tail cuff system (CODA, Kent Scientific). Measurements were taken before pump implantation and on days 3, 7, 14, 21, and 28 after implantation. Mean arterial pressure increased from 133.8 ± 21.2 mmHg before pump implantation to 169.4 ± 20.3 mmHg on day 28. Systolic and diastolic pressures rose in a similar manner. Although the blood pressure increased in a manner similar to the mice, no aneurysms were observed in any of the rats. This may be due to species differences that affect vessel thickness and metabolic rate. Further investigations will be needed to determine why ApoE rats become hypertensive due to AngII, but do not develop suprarenal dissecting aortic aneurysms
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